What is the predicted order of first ionization energies from highest to lowest for lithium (Li), sodium (Na), potassium (K), and rubidium (Rb)?

Lithium, sodium, potassium, and rubidium are all in Group 1. First ionization energy generally decreases down a group because the outer electron is farther from the nucleus and more shielded by inner electrons, so it is easier to remove. Thus the order from highest to lowest is Li > Na > K > Rb, which is choice C.

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